The invention relates to ultrasonic transducers and more particularly ultrasonic transducers of the Tonpilz arrangement in which a stack of piezoelectric ceramic driver elements or disks are stacked in push-pull relation and held together between a heavy mass element such as a steel disk and an aluminum coupling element with the piezoelectric ceramic disks being excited in push-pull relation so as to allow for higher exciting voltages. The sandwich is held together by a prestress bolt. Such a system is disclosed in Antonevich U.S. Pat. No. 3,370,186 from which FIGS. 1 and 2 hereof have been taken. In Antonevich, the output member is a perforated metal member which takes the form of a labyrnith structure or any of a variety of cross-sectional forms and degree of perforation to provide predictable acoustical impedance. For example, the member may be built up of tubular members metalurgically bonded to the base or the member may take the form of a honey-comb structure set into a proper base.
According to this invention a pair of laminar graphite epoxy sheets adhesively sandwiched to the opposite sides of a honeycomb core provides an extremely low mass but extremely rigid plate member which is secured either by an adhesive such as an epoxy adhesive to an aluminum plate at the output end of the stack of electrostrictive elements. Thus, the ultrasonic transducer ensemble comprises a mass which preferably is a steel disk to provide a null, a stack of piezoelectric ceramic driven disks connected in push-pull relation to allow higher voltages on the ceramics to enhance more energy input thereto, a lower mass aluminum disk so that the piezoelectric driver disk are sandwiched between a steel metal mass and an aluminum metal mass and drawn tightly together by a prestressed tie rod member or bolt; and, according to the invention, the coupling of the ultrasonic energy from the output end of the stack of piezoelectric ceramic driven disks is by means of a rigid, light weight, low mass member having a pair of rigid laminates adhesively sandwiching a light-weight structure which preferably is a honeycomb oriented in a direction coaxial with the axis of the stack of ceramic disks and boundedly secured at each honeycomb end to the laminates so that the shear modulus is extremely high and the density of the composite structure is thus very low so that the lateral or outer ends of the laminate cannot flap or move out of phase with the central portion. The velocity of the shear wave in the honey-comb thus is made as high as possible. In operation, the metal mass reflects the energy into the ceramic mass and the mass thus acts as a node so that all energy iss delivered to the front end where there is a very low or no mass. There is less loss of energy in the transducer per se and more energy is efficiently coupled to a load because of the larger surface of the laminates contacting the fluid medium. In air, the transducer has an especially good impedance match resulting in a longer range for essentially the same energy input as compared to prior art systems.